VOL. LVII.] PHILOSOPHICAL TRANSACTIONS. 455 



the billows from a wide ocean, heap up the coral with which those seas are filled. 

 This, obvious after storms, is perhaps at all other times imperceptibly effected. 

 The coral banks, raised in the same manner, become dry. These banks are 

 found of all depths, at all distances from shore, entirely unconnected with the 

 land, and detached from each other: though it often happens that they are 

 divided by a narrow gut, without bottom. 



Coral banks also grow, by a quick progression, towards the surface; but the 

 winds, heaping up the coral from deeper water, chiefly accelerate the formation 

 of these into shoals and islands. They become gradually shallower, and when 

 once the sea meets with resistance, the coral is quickly thrown up by the force 

 of the waves breaking against the bank; and hence it is that, in the open sea 

 there is scarcely an instance of a coral bank having so little water that a large 

 ship cannot pass over, but it is also so shallow that a boat would ground on it. 

 Mr. D. has seen these coral banks in all the stages; some in deep water, others 

 with a few rocks appearing above the surface, some just formed into islands, 

 without the least appearance of vegetation, and others, from such as have a few 

 weeds on the highest part to those which are covered with large timber, with a 

 bottomless sea at a pistol shot distance. 



The loose coral, rolled inward by the billows in large pieces, will ground, and 

 the reflux being unable to carry them away, they become a bar to coagulate the 

 sand, always found intermixed with coral ; which sand, being easiest raised, will 

 be lodged at top. When the sand bank is raised by violent storms, beyond the 

 reach of conjmon waves, it becomes a resting place to vagrant birds, whom the 

 search of prey draws thither. The dung, feathers, &c. increase the soil, and 

 prepare it for the reception of accidental roots, branches, and seed, cast up by 

 the waves, or brought thither by birds. Thus islands are formed: the leaves 

 and rotten branches, intermixing with the sand, form in time alight black mould, 

 of which in general these islands consist, more sandy as less woody; and when 

 full of large trees, with a greater proportion of mould. Cocoa nuts, continuing 

 long in the sea without losing their vegetative powers, are commonly to be found 

 in such islands ; particularly as they are adapted to all soils, whether sandy, rich, 

 or rocky. 



The violence of the waves, within the tropics, must generally be directed to 

 two points, according to the monsoons. Hence the islands formed from coral 

 banks, must be long and narrow, and lie nearly in a meridional direction. For 

 even supposing the banks to be round, as they seldom are when large, the sea, 

 meeting most resistance in the middle, must heave up the matter in greater 

 quantities there than tcnvards the extremities: and, by the same rule, the ends 

 will generally be open, or at least lowest. They will also commonly have 

 soundings there, as the remains of the banks, not accumulated, will be under 



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